1. Field of the Invention
The invention relates to electronic driving devices, and particularly to a device for driving discharge lamps in a light source module of a liquid crystal display (LCD) panel.
2. Description of Related Art
Conventionally, a liquid crystal display (LCD) panel uses discharge lamps, such as cold cathode fluorescent lamps (CCFLs), as a light source of a backlight system. Typically, an inverter circuit outputs an alternating current (AC) signal to drive the CCFLs. If voltage of the AC signal output from the inverter circuit is too great, the CCFLs may be damaged; and if the voltage of the AC signal output from the inverter circuit is too low, the CCFLs cannot be started. Therefore, a voltage sensing circuit and a protection circuit are required in the inverter circuit.
Referring to FIG. 4, a block diagram of a conventional driving device 10 for driving a light source module 140 is shown. The driving device 10 includes a driving circuit 100, a transformer circuit 110, a protection circuit 120, and a voltage sensing circuit 130. The transformer circuit 110 outputs an AC signal to the light source module 140. The voltage sensing circuit 130 reads a magnitude of voltage of the AC signal via capacitors C1, C2, and C3 thereof. If the magnitude of the voltage is too great after rectification of the voltage signal by a half-wave rectifier D1 of the voltage sensing circuit 130, the voltage sensing circuit 130 directly outputs an over-voltage signal to the protection circuit 120. However, the driving device of FIG. 4 fails to provide under-voltage protection.
FIG. 5 is a block diagram of another conventional driving device 10′ for driving a light source module 140. Modules of the driving device 10′ are substantially the same as those of the driving device 10, except a voltage sensing circuit 130′ and a protection circuit 120′. The voltage sensing circuit 130′ reads a magnitude of the voltage of the AC signal output from the transformer circuit 110 via capacitors C1, C2, and C3 of the voltage sensing circuit 130′. If the voltage signal is abnormal, after a half-wave rectifier D1 rectifies the voltage signal and diodes D2 and D3 divide the voltage signal, the voltage sensing circuit 130′ outputs an under-voltage signal or an over-voltage signal to the protection circuit 120′. However, this device is susceptible to interference, and circuit impedances thereof are high.